What Causes Weathering of an Arch?

Written by peggy madsen
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What Causes Weathering of an Arch?
A natural arch weathered by erosion. (sea arch image by Chris Bibbo from Fotolia.com)

A natural arch is a rock formation with a hole going completely through it. Erosion and other natural processes, working in concert or individually, initially form the arch. Weathering of an arch occurs due to various forms of macroscopic and microscopic erosion. Biological and chemical actions also can weather arches. Many of the forces that cause rock weathering are also responsible for arch formation.

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Microscopic Erosion Through Chemical Exfoliation

Snow, ice or seeping water can permeate an arch's rock, resulting in weathering by chemical exfoliation on a microscopic level. The seeping water dissolves crystalline grains that have held the rock together. Wind, water or gravity removes the loosened particles of the rock. Acids in biological agents also can cause chemical weathering.

What Causes Weathering of an Arch?
Seepage can cause chemical exfoliation. (cracked earth image by nicolasjoseschirado from Fotolia.com)

Macroscopic Erosion

An arch can become weathered when fractures in the arch's rock become wider and break off into large pieces, a process known as macroscopic erosion. Earthquakes can cause such fractures and erosion. Thermal exfoliation is defined as macroscopic fractures and breakage due to temperature fluctuations. Water or gravity acts to move the macroscopic pieces away from the arch's main mass. Macroscopic erosion is also known as mechanical weathering.

What Causes Weathering of an Arch?
Rock fractures. (Rock cracks 20080426-1180075 colour image by SIGNSofMIND from Fotolia.com)

Wind

Wind is a form of microscopic erosion. Intense winds may sandblast rock by picking up grains of sand and pounding them against the rock, thereby smoothing the arch's surface.

What Causes Weathering of an Arch?
Sand and wind erode rock. (Blow image by DDP from Fotolia.com)

Water Flow

A constant flow of water from streams and rivers can cause physical weathering by cutting a path into an arch's rock. The advance and retreat of waves and glaciers also cause physical weathering.

What Causes Weathering of an Arch?
Physical weathering caused by glaciers. (Glacier in Glacier Bay National Park image by Don Lewis from Fotolia.com)

Biological Weathering

Natural rock arches can weather due to plant or animal growth. These life forms excrete acidic organic materials that etch the rock, and plants grow roots that can cause fractures in the rock. Iron-oxidising bacteria may also weather rock on the microscopic level.

What Causes Weathering of an Arch?
Plant growth weathers arches. (arch image by A74.FR Ben Fontaine from Fotolia.com)

Freeze-Thaw Weathering

Cold climates with days that hover around the freezing point of water can cause freeze-thaw weathering, in which liquid water flows through cracks in rock and then freezes at night. The expansion of freezing water forces the arch's rock apart, and macroscopic pieces break off. This form of physical weathering is also called frost shattering or freeze expansion.

What Causes Weathering of an Arch?
Freezing ice can part the rock in an arch. (Ice image by Einar Bog from Fotolia.com)

Warm Climate Exfoliation

Fluctuating temperatures in very warm climates can cause exfoliation of an arch. When rock is heated (to relatively high temperatures) and cooled repeatedly, physical weathering occurs.

What Causes Weathering of an Arch?
Weathering in very warm climates. (Oasis de Chekiba image by albillottet from Fotolia.com)

Gravity

Permeable rocks, such as limestone, sandstone and chalk, allow water to pass through them. When permeable rock is eroded by flowing water, an arch resting on it can fall due to gravity alone.

What Causes Weathering of an Arch?
Limestone rocks. (limestone islands 1 image by Pierrette Guertin from Fotolia.com)

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